Caption: Used and unused toothpicks. Coloured scanning electron micrograph (SEM) of an unused (left) and a used (right) toothpicks. The used toothpick has a blunt end and is covered in dental plaque. Plaque consists of a film of bacteria embedded in a glycoprotein matrix. The matrix is formed from bacterial secretions and saliva. Plaque is the main cause of tooth decay. The bacteria feed on sugars in food, producing acid as a waste product. This acid corrodes the teeth's enamel coating, resulting in dental caries. A build-up of dental plaque can also lead to inflamed and infected gums. Severe gum disease can lead to teeth falling out. Magnification: x20 when printed at 10 centimetres wide.